Hahaha - the set-up for the video was a bit longer than the video itself. The normal rubber bands - all I had to do was a bit of shifting on the open side, and the other three sides of the box had enough friction to keep it more or less in tunes.
The tension on the exercise bands (the bass) was much more difficult (you can see the box is nearly breaking!), so I had to tie a knot in each one to at least get it closer, and then shift it again just before I pressed record!
It's just that it looked like the box was screaming for you to set it free hahahahahaha. Crazy, but at least it got the job done. very ingenious 🤜🏼🤛🏼